A process of forming a thin film on a substrate in a process container of a substrate processing apparatus may be performed in manufacturing a semiconductor device. Subsequently, a cleaning process of supplying a cleaning gas into the process container and etching away deposits including thin films deposited in the process container may be performed. An example of the cleaning gas may include a fluorine (F2) gas. The F2 gas can be used to remove deposits since it has an extremely high reactivity to allow the cleaning process to be easily performed through pyrolysis.
However, in order to use the F2 gas to etch a deposit including, for example, a silicon nitride (Si3N4, simply SiN) film formed by thermal CVD (Chemical Vapor Deposition) at a practical speed, there is a need to heat the process container to a relatively high temperature. In this case, while the deposit formed in the process container is etched, a quartz (SiO2) member in the process container may also be etched.
To overcome this problem, it is considered that a mixture of F2 gas and nitrogen monoxide (NO) gas is used as the cleaning gas. The mixture of F2 gas and NO gas can prevent the quartz member from being etched since the deposit can be etched with the process container held at a relatively low temperature, as compared to the case where the F2 gas is used alone.
However, from careful studies by the present inventors, it has proved that the mixture of the F2 gas and the NO gas may generate exothermic energy by reaction of these gases and components of a substrate processing apparatus may be damaged by this exothermic reaction. For example, when the F2 gas and the NO gas are mixed in a gas supply pipe and are supplied into a process container, the exothermic reaction is produced in the gas supply pipe, which may result in corrosion of the gas supply pipe. In addition, if the F2 gas and the NO gas are separately supplied into the process container and mixed in the process container, a local exothermic reaction is produced in the process container, which may result in a partially etched quartz member in the process container. In both cases, particles such as corrosion products or the like may be transported into a process chamber along with the gases and particles such as quartz powders and so on may be produced in the process chamber, which may lead to product defects. These problems are first revealed by the careful studies of the present inventors.